Table 2 Methodological information for dealing with zero-events studies

1) In the systematic review, did any meta-analysis contain zero-events studies?

406 (63.44, 59.57 to 67.18)

88 (13.75, 11.18 to 16.66)

146 (22.81, 19.62 to 26.26)

640

2) If zero-events studies were involved, what were the types of zero-events studies?

406

• Single-arm-zero-events only

174 (42.86, 37.99 to 47.83)

‐

‐

• Double-arm-zero-events only

7 (1.72, 0.70 to 3.52)

‐

‐

• Both single and double

208 (51.23, 46.25 to 56.19)

‐

‐

• At least containing single-arm-zero-events study

7 (1.72, 0.70 to 3.52)

‐

‐

• At least containing double-arm-zero-events study

8 (1.97, 0.85 to 3.85)

‐

‐

• Cannot be judged

2 (0.49, 0.06 to 1.77)

‐

‐

3) If zero-events studies were involved, whether the authors specified methods to deal with zero-events studies?

131 (32.27, 27.74 to 37.05)

275 (67.73, 62.95 to 72.26)

0 (0.00, 0.00 to 0.90)

406

4) If the authors specified methods, whether they clarified reasons for selecting the method for zero-events studies?

44 (33.59, 25.58 to 42.36)

87 (66.41, 57.64 to 74.42)

0 (0.00, 0.00 to 2.78)

131

5) If zero-events studies were involved, how zero-events studies were dealt with by the authors?

• Discarding single-arm-zero-events studies (174 + 208 + 7 = 389)

3 (0.77, 0.16 to 2.24)

384 (98.71, 97.03 to 99.58)

2 (0.51, 0.06 to 1.85)

389

• Discarding double-arm-zero-events studies (7 + 208 + 8 = 223)

170 (76.23, 70.09 to 81.66)

50 (22.42, 17.12 to 28.47)

3 (1.35, 0.28 to 3.85)

223

6) Whether a sensitivity analysis was employed through at least one different synthesis method for dealing with zero-events studies?

53 (13.05, 9.93 to 16.73)

353 (86.95, 83.27 to 90.07)

0 (0.00, 0.00 to 0.90)

406

7) For those failed to synthesize studies with zero-events, did the authors discuss about the potential impact of such studies (e.g., discarding them) on the results?

22 (12.94, 8.29 to 18.94)

148 (87.06, 81.06 to 91.71)

0 (0.00, 0.00 to 2.15)

170